Preservation of tanned leather



Patented June 13, 1939 UNITED STATES 2,162,015 PRESERVATION F TANNED"LEATHER Alfred W. Hoppenste'dt, Buffalo, N. Y., assignor'to "J. A. WebbBelting 00., 1110., Buffalo, N. Y.

No Drawing. Application September 23, 1936, Serial ,No. 102,255

Claims.

This invention relates to the preservation of tanned leather, andit hasparticular reference to a method of, and means for, preventing the .de-

ter ioration of leather from those causes com- 5 monly termed rot.

The word-leather, as generally used and as employed in' thisspecificatiomconnotes the product resulting from the treatment of hidesor skins with various media t'e'r'me'd tanning agents, which convert thehides into a more durable and less putrescible condition. Leather, as aproduct of tanning operations, finds many industrial uses, suchasinpower transmission belting, coverings; and the like. Over a periodoftime, however, leather loses its strength and resiliency, and becomesdry, powdery,- and actually disintegrates. Leather in such condition issaid to be rotten, and the causes of the decaymay generally be termedrot. Rot in leather may be caused in various ways, as, for example, bycontact-of the leather with harmful chemicals. It has been observed thatvegetable tanned leather is notably susceptible to deterioration fromthis source, Rot may also be causedby physical means. For example,excess heat will causeleather to disintegrate. In leathers formechanical purposes where stress and strain and friction of the fibersare present, excessive oil' or grease on the leather, or insufficient orlow grade oil or grease may cause disintegration of the fibers andsubstance of the leather. Users of beltsclassify variousspecies of decayaccording to appearance and texture by such terms as oil rot, dryrotfland red rot while bookbinders and other leather workers employ theterms dry rot and red rot.

I have'disc'overed that rot, particularly insofar as it is induced bychemical action, may be counteracted and prevented if the tanned leatheris 40 occasionally treated with a composition having the power topenetrate the pores of the leather and also having a basic reactivecharacter. As a further specification of suitable means to prevent orcounteract rot, I have discovered that its effects may be offset byneutralizing the ingredients producing rot with a suitable solution ofone of the class of substances known as organic bases, the solvent beinga medium which is comparatively inert chemically, but physically able topenetrate the pores of the leather.

I attribute the beneficial results obtained by such treatment to thefact that normal or healthy leather has an acid or pH value, asdetermined by the hydrogen-ion concentration method, of about 3 to 4.That is to say, if a number of samples of healthy leather, as preparedby various tanning methods, be extracted with water, and the extracttested in the usual ways-the pH values of the solutions will fall inthis range,-thus showing that normal leather is pronouncedly acid. 5However, if the pH value falls below say 2.95 to 3.0, and particularlyas low as say 2.35, the leather shows all the effects symptomatic ofrot. That is to say, while healthy leather is acid, rotten leather ismore acid in nature,'and it may be said that the condition of rot inleather is caused by the absorption, as from the atmosphere, of acidcarbonic or sulphur vapors.

Accordingly, the present invention contemplates the treatment ofleather, Whose pH value has dropped into the danger zone, with apenetrating solution of an organic base, so that the absorbed acids maybe neutralized, and the leather restored to its normal acidrange. It hasbeen found that leather having a normal or slightly sub-normal acidvalue may be so treated to prevent any development of rot, While leatherhaving a somewhat increased acid content may be treatedto oflfset the"effects of rot, thus curing the condition, provided, of course, it hasnot advanced too far.

The general chemical class called organic bases includes such substancesas the primary, secondary, and tertiary amines, the amino-com pounds oraromatic amines, and the Vegetable bases or pyridine nucleus compounds.To name some of the species of these groups, it may be stated that thefollowing have been found effica'cious: mono--, di-, and tri-amylamine,triethylene tetramine, anilin, toluidine, xylidine, pyridine, andquinoline. These compounds (whichever may be selected, or a kindredcompound havinglike desirable properties) are dissolved in a suitablesolvent which is chemically inert to the leather, such, for example, ascarbon tetrachloride, benzol, butanol, naphtha, or turpentine. Thevarious chlorinated organic solvents may also be used, but care shouldbe taken in such event to select one which, upon any decomposition, willnot develop a free acid. It is preferred to employ as a solvent amaterial which will not dissolve the cement (such as animal glue ornitrocellulose) which may be used in making a multi-ply leather product,such as a belt. The solvent should also penetrate the pores of theleather quickly, yet not react with the bonding media between thefibers. It may also have a relatively low boiling point and benon-flammable, so that, upon application of the dissolved compound, thesolvent may safely vaporize and leave 2 behind the organic base to reactwith the absorbed acids.

Since the amount of free acid required to change the pH value of leatherfrom say 3.0'to

2.9 is very small, it will be apparent that fairly dilute solutions ofthe organic base may be employed, the exact concentration of base insolution and the amount of solution used depending upon the activity ofthe compound selected, and the probable amount'of acid absorption over agiven period of time. it will be found that effective preservation maybe obtained by brushing or swabbing the surface of the leather with thesolution, say every si months.

In order to indicate the relative strengths of s 1 b f i o ution e ore ater Solvent solute strength treattreatment ment 7 Percent BenzolMonoa1nylarnine 6 2. 75 3.15

D0 Diamylamine 20 2.37 3.06 Gasoline 'Triamylamine 30 2.45 3.17 ToluolTriethylene-tetra- 4 2. 70 3.30

mine.

D0 do l2 2. l0 3. l0 Turpentine Anilin 10 2. 65 3.00 Naphtha Xylidin l42. 65 2. 95 Toluol-butanoL- Pyridine 6 2.80 3.17 Xylol l. Quinoline 102.85 3.20

- It will be observed that in each case, a leather having an acid valuesynonymous with a condition of rot was restored to a normal or healthycondition; thus preventing the, development of further rot, and it willalso be noted from the compounds used that the function of preventingsuch rot is common to widely selected members of the class of organicbases. It will also be noted that the solvents employed are not harmfulto the leather, and that they do not include water,

since water has a deleterious eifect on leather if allowed to penetratethe pores.

In this connection it may be noted that some forms of belt dressings aremiscible with the basic solutions of the present invention, whichsuggests making a suitable mixture so that the belt dressingandrpreservative are applied concurrently. However, since it is a simplematter to swab the belt with the preservative and rot For ordinarycommercial use,

inhibitor, and a mixed solution might have so high a viscosity as toprevent complete penetration, this suggestion, while feasible, is not tobe recommended too strongly. t

I am, of course, aware of the fact that heretofore it has been proposedto load leather during the tanning process with inert ingredients toprotect the finished product against rot, and that proposals have beenadvanced to employ organic bases as ingredients of tanning baths.However, the present invention contemplates leather as it exists incommerce, and further contemplates the treatment of diseased leatherwith a reactive organic base, rather than with the reaction product ofsuch a compound which, at the time of application, has lost itscorrective virtues.

It will therefore ,be understood that I do not claim merely thecontacting of raw or partially prepared hides with organic bases ortheir reaction products, but what I do claim is:

1. The method of correcting and inhibiting a condition of rot in tannedleather, which comprises applying to the surface of such leather apenetrating solution of an organic nitrogenous base in an inert organicsolvent.

2. The method of correcting and inhibiting a condition of rot in tannedleather, which comprises impregnating such leather with an organicnitrogenous base in a quantity sufficient to raise the pH value of theleather to between 3.0 and 4.0.

3. The method of correcting and inhibiting a 4 condition of rot intanned leather which coml f prises treating a piece of tanned leatherwhose pH value is less than 2.95 with a penetrating none aqueoussolution of an organic nitrogenous base in an amount sufficient to raisethe pH value to more than 2.95 but less than 4.0.

4. In the preservation of leather, the process which comprises selectinga piece of leather which has been subjected to an acid atmosphere to anextent sufiicient to reduce its pH value to less than 3.0, andimpregnating such leather with a solution of a reactive organicnitrogenous base in ,a

volatile organic solvent chemically inert with respect to the leather inan amount sufiicient to restore the pH value to between 3.0 and 4.0.

5. The method of correcting and inhibiting a condition of rot in tannedleather which comprises treating such leather with anorganic nitrogenousbase typified by the class of compounds including amylamine,ethylene-tetramine, anilin,

xylidin, pyridine, and quinoline and dissolved in a non-aqueous organicsolvent, said treatment being with a quantity suflicient to increase thepH value of such leather to more than 2.95 but less than 4.0.

ALFRED W. HOPPENSTEDT.

